1. Field of the Invention
The present invention relates to an image reading apparatus such as image scanner, facsimile apparatus, composite apparatus (or multifunction apparatus), copying apparatus, or the like having a function for reading images, or to an image reading unit of them.
2. Description of the Related Art
Hitherto, various systems have been devised with respect to an apparatus such as image scanner, facsimile apparatus, composite apparatus, copying apparatus, or the like having a function for reading images. In those image reading apparatuses, as a scan driving unit of a reading and scanning unit, there are various systems such as a system using a belt, a system using a wire, a system using a rack provided in the scan direction and a pinion gear which is engaged therewith (for example, refer to Japanese Patent Application Laid-Open No. 2004-054283), and the like.
Among those systems, in Japanese Patent Application Laid-Open No. 2004-054283, there is disclosed a technique in which for the driving using the rack and the pinion gear, a separating force of the rack and the pinion gear is used as a force adapted to press the reading and scanning unit to a guide rail of the scan. In Japanese Patent Application Laid-Open No. H07-184008, there is disclosed an image reading apparatus in which a pressing unit to the guide rail is separately provided in order to press the reading and scanning unit to the guide rail of the scan.
In the case of using the separating force of the rack and the pinion gear as a force adapted to press the reading and scanning unit to the guide rail of the scan, ordinarily, by changing a pressure angle of 20° of the gear to, for example, 30°, the force adapted to press to the guide rail (guiding force) can be increased. Thus, it is enabled to be hard to receive an influence of the vibration or the like. However, if the guiding force is increased by increasing the pressure angle, at the same time, a driving force adapted to scan-drive the reading and scanning unit is decreased and a driving efficiency is deteriorated. Generally, in order to reduce the driving force, a frictional force of the guide rail is controlled to a small value by using a low frictional material or the like. Since the separating force of the gear is in almost direct proportion to a coefficient of friction, if the frictional force is small, the separating force is small and the stable guiding force cannot be obtained. According to the construction in which the pressing unit to the guide rail is provided, since the number of parts increases, it is difficult to miniaturize the apparatus.
According to a type in which a motor for scan-driving is provided on the reading and scanning unit, a signal line to drive the motor is distributed from the apparatus main body to the reading and scanning unit and the motor is driven while pulling the signal line. Therefore, a force is applied to the reading and scanning unit from the signal line, so that the reading and scanning unit is moved in the inclined state or is unstable and liable to be influenced by the vibration or the like.